The episode title is a reference to some of the characters: Summer of 4 (Homer, Marge, Bart and Maggie) ft 2 (Milhouse and "New" Lisa)
The name of this episode is also a reference to the movie Summer of '42.
The last school day begins at 9:00 am and ends at 3:00 pm.
On Australian TV, the scene of Homer buying the risque personal items (the condoms, the porno mags, two enemas, some panty shields, and a bottle of Old Harper) to cover his tracks in buying illegal fireworks was cut, yet the scene of Marge picking through the bag and telling Homer, "Whatever you're planning to do tonight, count me out!" wasn't edited.
The firecracker that Homer attempts to use to celebrate the Fourth of July (and is later forced to use in the washing machine, rupturing a disposal pipe in the process) is called the M-320. That's also the name for a grenade launcher.
This episode was broadcast on the same day as the episode "Homerpalooza" on American TV.
When Milhouse sees Lisa in her cool persona, he remarks that she looks like Blossom. Coincidentally, fourteen years after this episode aired Blossom's actress Mayim Bialik, would be cast as The Big Bang Theory character Amy Farrah Fowler, who like Lisa is very intellectual and has a similar disappointing yearbook experience due to unpopularity like Lisa in this episode.
At the end of this episode, a Beach Boys song plays at the end credits and when the Gracie Films logo appears, the logo's music is played by a sax and it is a summer-like theme.
In the promotional image for this episode, Lisa's glasses have no or transparent lenses, but in the episode itself, they have purple lenses.
When Lisa first meets the skater kids, she's wearing her glasses in one shot but they disappear in the next. Then they reappear in front of the library.
When Lisa gets to the new city to make friends, none of them go to school. Kids have to spend at least 15 hours a week going to school. The episode was set during summer break.
At Ned's beach house, there is a picture of Maude above the bed Lisa was sitting on. When the camera angle changes, the picture changes to a photo of Rod and Todd.